August 30, 2022

How can rootstock grafting make coffee plants more resilient?


The effects of climate change are becoming more and more of a concern for the coffee industry – particularly for farmers. 

Findings from a research paper published earlier this year conclude that four of the five top coffee-producing countries in the world will see the amount of land suitable for coffee production fall by 2050. It’s believed that coffee will be one of the worst-affected crops around the world as far as the effects of climate change are concerned – leaving some farmers even more vulnerable than they currently are.

However, there are a number of things that can be done at farm level to mitigate the impact of climate change. One of these is rootstock grafting. When executed successfully and in the right way, this can help coffee plants become more resilient to extreme weather.

So, what is rootstock grafting and how does it work? I spoke to two people involved in the BOLERO project (Breeding for coffee and cocoa root resilience in low input farming systems based on improved rootstocks), an €8.5 million EU-funded initiative under Horizon Europe, to learn more. Read on to find out what they said.

You may also like our article on how grafting arabica to robusta can improve coffee yields.

coffee seedlings at different stages of growth

What are rootstocks?

In order to graft coffee plants successfully, we must first understand the different parts of the plant. 

The rootstock comprises the roots and stem segments that grow under the soil, which are essential for supporting the plant and absorbing nutrients. The scions are the offshoots or twigs that grow above ground – these contain the plant’s genetic material that determine which types of flower and fruit will grow.

Fabrizio Arigoni is the Head of Plant Science at Nestlé Research. 

“A plant’s root system is an important part of assessing adaptability to stressors, such as disease and drought,” he explains. “Grafting allows you to create more resilient plants by combining together complementary coffee species or varieties.”

For example, grafting an arabica scion onto a robusta rootstock is a common way of strengthening the root system of an arabica plant. This is because robusta rootstocks are larger and stronger, which means the plant can then absorb more water and nutrients.

Benoît Bertrand is a geneticist at French agricultural research organisation CIRAD.

“The practice of grafting rootstocks is commonly used with many crops, including citrus plants, apple trees, and vines,” he says.

So how does rootstock grafting work?

“Rootstock grafting is when you connect the upper part of one plant to the root system of another,” Fabrizio says. 

Essentially, after the plant has been growing for 50 to 70 days, a small incision is made below the plant’s first leaves. The rootstock and scion are then taped together and left to grow into each other.

“In the grafting process, rootstocks will dictate the development of the rooting system – the branching and its horizontal and vertical extensions,” Fabrizio adds.

However, it is advised that only those with the required knowledge and experience carry out rootstock grafting, as it is delicate and complex.

women tend to coffee seedlings at a nursery

Why is rootstock grafting so important?

Rootstock grafting is not a new practice; it’s been carried out since the late 19th century. However, it is arguably becoming more necessary than ever for the coffee sector.

“Coffee production is under threat of disease and drought, which are both exacerbated by climate change,” Fabrizio explains. “This can mean that farming is becoming increasingly more challenging for some producers.

“A recent study showed that by 2050, all main coffee-producing countries will be seriously affected by drought and rising temperatures – with a potentially dramatic effect on coffee production,” he adds. “Moreover, global coffee consumption is increasing, which puts pressure on the global supply chain.”

Among a number of other sustainability techniques implemented on coffee farms, including agroforestry, research has shown that successful rootstock grafting can benefit coffee plants by making them more resilient to extreme weather.

“Numerous scientific studies show that grafting well-selected rootstocks can help coffee plants adapt to difficult soil and/or climate conditions,” Benoît explains. “Rootstock grafting can allow plants to adapt better to higher temperatures, prolonged drought, excess water, and higher aluminium levels (which causes toxicity in many soils).

“Rootstock varieties can be fast and effective at mitigating the effects of global warming for both robusta and arabica, without no effects on quality or yields,” he adds.

Benoît also says that rootstock grafting can provide coffee plants with better protection against certain pests and diseases – some of which are becoming more prevalent as a result of climate change

“When cultivating arabica coffee, rootstock grafting is used to protect plants against nematodes,” he explains. These are small parasitic worms which can drain nutrients from the root systems of coffee plants, thereby inhibiting growth.

Furthermore, as rootstock grafting helps coffee plants to absorb more nutrients, this means the use of fertilisers becomes less necessary.

“Fertilisers contribute to around 20% of the total carbon footprint of the overall agricultural industry,” Fabrizio says. “Furthermore, nitrogen has the highest levels of greenhouse gas emissions [out of all fertilisers] because the production process is energy-intensive, but also because emissions continue after the fertiliser is applied to the soil.”

elderly woman harvests coffee cherries

Improving farmer resilience

We know that the extreme and erratic weather caused by climate change occurs most prominently in equatorial and tropical regions. This is also where the vast majority of the world’s coffee is grown.

As such, helping coffee farmers become more resilient is vital if we are to secure a future for the coffee industry.

“A coffee farm is a small enterprise, and the farmer’s income depends on the balance between input and output,” Fabrizio says. “The BOLERO project aims to cultivate coffee plants that are better adapted to climate change, so they can be offered to farmers to make their livelihoods more resilient.”

Benoît explains more about the project, which is being carried out by CIRAD. Some of the project’s 18 partners include larger companies (such as Nestlé, Jacob Douwe Egberts, Lavazza, illycaffè, and ECOM Trading) coffee institutes (such as WASI, NACORI, CATIE, and Promecafe), and several prestigious European universities.

“The objective of the BOLERO project is to develop rootstocks for robusta and arabica plants,” Benoît tells me. “CIRAD will then assess whether these rootstocks can increase carbon fixation, decrease water usage, and increase nitrogen consumption.

“The project will also assess whether the microbiome (the community of microorganisms, such as bacteria, fungi, and yeasts) in the roots of the coffee plants is improved by rootstock grafting,” he adds. 

Fabrizio tells me: “Participating in the BOLERO project has been a unique opportunity for Nestlé to collaborate with and share knowledge and expertise on coffee research with a larger community of people, such as CIRAD.

“Contributors to the BOLERO project all have different areas of expertise, including plant physiology, plant genetics, genomics, and breeding,” he adds.

The project, which will begin in October 2022, will take place on coffee farms in Vietnam, Nicaragua, and Uganda. Benoît explains why rootstock grafting is essential for coffee production in these countries.

“In Vietnam, producers frequently graft robusta onto liberica,” says Benoît. “Meanwhile, in Uganda, global warming is already affecting robusta production. 

“Finally, in Nicaragua, CIRAD will evaluate whether grafting robusta to arabica will help to protect plants from increasingly frequent episodes of drought and high temperatures,” he adds. “We will use both robusta and wild coffee species to develop rootstocks.”

By using wild coffee species in rootstock grafting, researchers may also have a better change of protecting the lesser-known species in the Coffea genus; it’s estimated that as many as 60% of these species could be at risk of becoming extinct because of climate change.

ripe and unripe cherries on a coffee tree

Looking ahead to the future

Climate change is a complex problem of immense proportions that bears a significant threat for the future of the coffee industry. However, it’s clear that preventative practices like rootstock grafting can help coffee farmers to adapt to ever-changing environmental conditions.

“Coffee rootstock research is crucial when it comes to mitigating the impact of climate change,” Fabrizio says. “It leads to the discovery of novel solutions that are sustainable and can be implemented at scale.”

Benoît agrees, telling me: “Rootstocks will considerably improve the productivity and climate adaptation of coffee plants.

“The grafting technique is very simple,” he says. “It’s already implemented on a large scale in some producing countries, such as Guatemala – including by smallholder farmers.”

But Benoît points out some of the issues that come with carrying out the technique.

“The real challenge is encouraging more producers to adopt this practice,” he says. “The price of seed is a major deterrent, so CIRAD wants to develop a new, [more accessible] seed.

“What’s more, observing root growth is always difficult with grafting,” Benoît adds. “To combat this, the Leibniz Institute of Plant Genetics and Crop Plant Research has developed near-infrared imaging to observe the roots of young plants.”

While this technology may not be accessible for all coffee farmers, CIRAD has also created another set of digital tools to support producers.

“On farms, we will use scanners developed by CIRAD to measure root growth over several years,” he adds. “The analysis will be carried out by artificial intelligence algorithms which were developed as part of the project.”

And alongside increasing climate resilience, rootstock grafting could even potentially improve coffee quality and flavour. For instance, a Gesha and Caturra hybrid known as CGLE 17 was cultivated on Colombian farms and sold for a price of US $75/lb at a 2021 auction – showing the potential to improve income.

coffee seedlings arranged in a plastic tray

Rootstock grafting has proven benefits for coffee farmers. If carried out successfully with the required knowledge and skills, it can be worth the initial investment – especially as coffee production is becoming more and more affected by climate change.

As long as less experienced producers seek the advice and support from qualified grafting professionals, this technique could be one of the best ways to mitigate the impact of climate change and secure the future of the coffee sector.

Enjoyed this? Then read our article on how agroforestry can help to secure the future of the coffee industry.

Photo credits: Nestlé, Benoît Bertrand

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Please note: CIRAD is a sponsor of Perfect Daily Grind.

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